// Copyright (c) 2018 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#ifndef STORAGE_LEVELDB_UTIL_NO_DESTRUCTOR_H_
#define STORAGE_LEVELDB_UTIL_NO_DESTRUCTOR_H_

#include <type_traits>
#include <utility>

namespace leveldb {

// Wraps an instance whose destructor is never called.
//
// This is intended for use with function-level static variables.
    template<typename InstanceType>
    class NoDestructor {
    public:
        template<typename... ConstructorArgTypes>
        explicit NoDestructor(ConstructorArgTypes &&... constructor_args) {
            static_assert(sizeof(instance_storage_) >= sizeof(InstanceType),
                          "instance_storage_ is not large enough to hold the instance");
            static_assert(
                    alignof(decltype(instance_storage_)) >= alignof(InstanceType),
                    "instance_storage_ does not meet the instance's alignment requirement");
            new(&instance_storage_) InstanceType(
                    std::forward<ConstructorArgTypes>(constructor_args)...);
        }

        ~NoDestructor() = default;

        NoDestructor(const NoDestructor &) = delete;

        NoDestructor &operator=(const NoDestructor &) = delete;

        InstanceType *get() {
            return reinterpret_cast<InstanceType *>(&instance_storage_);
        }

    private:
        typename
        std::aligned_storage<sizeof(InstanceType), alignof(InstanceType)>::type
                instance_storage_;
    };

}  // namespace leveldb

#endif  // STORAGE_LEVELDB_UTIL_NO_DESTRUCTOR_H_
